/Engine/Source/Runtime/Engine/Classes/SparseVolumeTexture/SparseVolumeTexture.h
Sets empty default data. This is used when caching/building is canceled but some form of valid data is needed.
void SetDefault ( EPixelFormat FormatA, EPixelFormat FormatB, const FVector4f & FallbackValueA, const FVector4f & FallbackValueB )